The availability of mobile networked computing devices, such as smartphones or tablet computers, has given rise to the deployment of location based services. Known devices are equipped with at least one wireless networking interface, which allows them to connect to wireless local area networks, WLAN, or cellular data transmission networks such as UMTS, HSDPA or LTE networks. Many known devices are further equipped with a Global Positioning System, GPS, receiver, which generally enables the location of the device to be computed if it can receive broadcast signals emitted from at least four distinct GPS satellites. The mobile devices are further equipped with computing means that enable them to run software applications, to receive, send and process data. Location based services typically use the location coordinates as determined by the GPS receiver to provide location specific data via the network to the user. While this solution is both useful and provides sufficient precision for outdoor use cases (an accuracy of about 10 meters is provided), it is not useful when the mobile device to which the location specific data is to be sent is located indoors. As no line of sight from the device to the GPS satellite system exists, the device cannot use GPS data to compute its position and to request location specific data from the network.
Indoor location determination systems have been proposed based on various technical approaches. It has been proposed to use either active or passive tags, whose presence can be detected by the corresponding detectors or emitters, installed at known locations in an indoor environment. Such solutions rely on a dedicated equipment infrastructure and inherently suffer, besides being costly to put into practice, from scalability issues. As a consequence, the use and adoption of such systems is limited.
Patent document US 2005/0243936 A1 discloses a method and system for determining user location in a wireless communication network. The method acquires, at a mobile device, an indication of the signal strength of a set of deployed access points, such as for example WLAN access points. By using a previously constructed radio map, which maps the received signal strengths to probabilities of being in a specific location within the coverage area of the access points, the method locates the receiving device as being at a location at which the probability of measuring the set of signal strengths is highest.
The disclosed system makes use of equipment that is in general already deployed in many indoor locations. Indeed, most buildings or public areas are covered by several WLAN access points, whose locations and geographical coordinates are known. The assumption on the receiving device is that it is equipped with a wireless network interface card, NIC, which is able to provide a received signal strength indication, RSSI.
While the disclosed method is promising, practical implementations using today's widely available smartphones or tablet computers, have failed to produce accurate location determinations. This appears to be due to unreliable RSSI values being provided by the operating systems of the mobile devices. While the disclosed system relies on the observation that the measured signal strength increases monotonically with the number of collected measurement samples, this is not true if the lack of measurements is due to the behavior of the measuring device or terminal itself.